**Abstract**

The geometry and relative energy of the seven low-lying electronic
states of ozone and the ground state of ozonide anion have been
determined in C_{2v} symmetry by the complete active space
self-consistent field (CASSCF) and the multireference
Møller–Plesset perturbation (MRMP) methods. The results
are compared with the photodetachment spectra of
O_{3}^{−} observed recently by Arnold et
al. (1994). The theoretical electron affinity of ozone is 1.965 eV,
which is 0.14 eV below the experimental result of 2.103 eV. The
calculated adiabatic excitation energies (assignment of Arnold et
al. in parentheses) of ozone are ^{3}A_{2} 0.90 eV
(1.18 eV),
^{3}B_{2}, 1.19 eV (1.30
eV), ^{3}B_{1}, 1.18 eV (1.45
eV), ^{1}A_{2}, 1.15 eV (∼1.6
eV), ^{1}B_{1}, 1.65 eV (2.05 eV),
and ^{1}B_{2}, 3.77 eV (3.41 eV),
respectively. Overall the present theory supports the assignment of
Arnold et al. However, the simple considerations of geometry and
energy are insufficient to determine a specific assignment of
the ^{3}B_{2} and ^{3}B_{1}
states. The dissociation energy of the ground state of ozone is
computed to be 0.834 eV at the present level of theory. The present
theory also predicts that none of the excited states lies below the
ground state dissociation limit of O_{3}.